The need to remain cost and performance competitive in the production of semiconductor devices has driven the industry to a continuing increase in device density with a concomitant decrease in device geometry. To facilitate the shrinking device dimensions, new lithographic materials, processes and tools are being considered. Typical lithographic processes involve formation of a patterned resist layer by patternwise exposing the radiation-sensitive resist to an imaging radiation. The image is subsequently developed by contacting the exposed resist layer with a material (typically an aqueous alkaline developer) to selectively remove portions of the resist layer to reveal the desired pattern. The pattern is subsequently transferred to an underlying material by etching the material in openings of the patterned resist layer. After the transfer is complete, the remaining resist layer is then removed. Currently, 248 nm and 193 nm lithography are being pursued to print sub 200 nm features.
To do this, tools with higher numerical aperture (NA) are emerging. The higher NA allows for improved resolution but reduces the depth of focus of aerial images projected onto the resist. Because of the reduced depth of focus, a thinner resist will be required. As the thickness of the resist is decreased, the resist becomes less effective as a mask for subsequent dry etch image transfer to the underlying substrate. Without significant improvement in the etch resistance exhibited by current single layer resists, these systems cannot provide the necessary lithography and etch properties for high-resolution lithography.
Another problem with single layer resist systems is critical dimension (CD) control. Substrate reflections at ultraviolet (UV) and deep ultraviolet (DUV) wavelengths are notorious for producing standing wave effects and resist notching, which severely limit CD control of single layer resists. Notching results from substrate topography and non-uniform substrate reflectivity, which causes local variations in exposure energy on the resist. Standing waves are thin film interference (TFI) or periodic variations of light intensity through the resist thickness. These light variations are introduced because planarization of the resist presents a different thickness through the underlying topography. Thin film interference plays a dominant role in CD control of single layer photoresist processes, causing large changes in the effective exposure dose due to a tiny change in the optical phase. Thin film interference effects are described in “Optimization of optical properties of resist processes” (T. Brunner, SPIE Proceedings Vol. 1466, p. 297, 1991), the teaching of which is incorporated herein by reference.
Bottom antireflective coatings or BARC's have been used with single layer resists to reduce thin film interference. However, these thin absorbing BARCs have fundamental limitations. For some lithographic imaging processes, the resist used does not provide sufficient resistance to subsequent etching steps to enable effective transfer of the desired pattern to a layer underlying the resist. The resist typically gets consumed after transferring the pattern into the underlying BARC and substrates. In addition, the migration to smaller sub-90 nm node feature sizes requires the use of an ultra thin resist (>200 nm) in order to avoid image collapse. In many instances where a substantial etching depth is required, and/or where it is desired to use certain etchants for a given underlying material, the resist thickness is insufficient to complete the etch process. In addition the radiation-sensitive resist material employed does not provide resistance to subsequent etching steps sufficient enough to enable effective transfer of the desired pattern to the layer underlying the radiation-sensitive resist and anti-reflective coating (ARC).
In many cases, where the underlying material layer to be etched is thick, where a substantial etching depth is required, where it is desirable to use certain etchants for a given underlying layer, or any combination of the above it would be desirable to employ an antireflective hardmask. The antireflective hardmask layer could serve as an intermediate layer between the patterned radiation-sensitive resist material and the underlying material layer to be patterned. The antireflective hardmask layer receives the pattern from the patterned radiation-sensitive resist material layer by reactive ion etching (RIE) followed by the transfer of the pattern to the underlying material layer. The antireflective hardmask layer should be able to withstand the etching processes required to transfer the pattern onto the underlying material layer. Furthermore, a thin antireflective hardmask layer is desirable to receive the pattern by RIE from the resist layer, especially if a thin resist are used. While many materials useful as ARC compositions are known, there is a need for improved antireflective hardmask compositions with high etch selectivity to the radiation-sensitive resist material and to the underlying material layer. Further, many of the known antireflective hardmasks are difficult to apply to the substrate, e.g., applying these ARC's may require the use of chemical vapor deposition (U.S. Pat. No. 6,316,167; U.S. Pat. No. 6,514,667). It would be advantageous to apply the antireflective hardmask material by spin-on techniques like conventional organic BARC currently used in manufacturing.
In addition, antireflective hardmask materials are difficult to remove after pattern transfer. Typically organic BARC are removed by a wet or dry ashing process. CVD deposited hardmask layers are difficult to remove without damaging the underlying dielectric substrate. Ideally, the antireflective hardmask materials can be removed easily by a wet strip with high selectivity to the underlying substrates.
Thus, it would be desirable to be able to perform lithographic techniques with high etch selectivity yet sufficient resistance to multiple etchings. Such lithographic techniques would enable production of highly detailed semiconductor devices.